This invention relates to manufacturing rotors or armatures for dynamo-electric machines such as motors, generators, and alternators that have been wound with coils of wire. Such armatures are typically wound by means of winders like those described in commonly-assigned U.S. Pat. No. 5,383,619 to Cardini et al., although it will be understood that the invention is equally applicable to armatures which have been wound by other types of winders.
It is common practice in the art to use automatic balancing machines at the end of a rotor production line to determine how unbalanced the rotor has become during the processing stages and to correct for this unbalanced condition by cutting away portions of the rotor stack to correctly distribute the masses around the longitudinal axis and the length of the rotor.
It would be desirable, however, to balance the rotor in a way that does not require the removal of large amounts of material from the outer surface of the rotor stack by milling or turning. The machining of material from an assembled rotor may disturb assembled component parts and may reduce the efficiency of the motor.
Another technique for balancing armatures involves the application of a resin material to the coils. The resin is applied in droplets to the armature at several locations to correct for the unbalance.
This approach has several drawbacks. The mass and placement of the droplet of resin are critical to correct for rotor unbalance. However, it is difficult to dispense the exact amount of liquefied resin at the correct location without spilling or spreading to undesired locations. This approach also adds costly and time-consuming manufacturing steps, e.g., heating the resin to a liquid state, precisely dispensing the liquefied resin, and subsequently curing the resin to a hardened state.
A final technique involves attaching balancing masses to the armature after the coils have been wound, and prior to the impregnation of the coils with resin. After the balancing masses are attached, the impregnation resin is applied to the both the coils and the balancing masses.
This technique also presents several disadvantages. First, prior to impregnation with resin, the wound coils do not offer a stable base for mounting a balancing mass. The individual wires in the coil are able to shift significantly, which may make it difficult to securely mount the balancing mass to the wires. For example, adhesives used to attach the balancing mass may break as a result of wire shifting, thereby causing the mass to change position or to detach from the rotor entirely.
Secondly, the technique of measuring the unbalance of the rotor and adding balancing masses prior to the impregnation with resin may not be effective to balance the rotor. The resin adds mass to the rotor which may significantly change its balance characteristics. Therefore, the impregnation step may introduce additional unbalance to the rotor, which would require repeating one of the techniques described above.
In view of the foregoing it is an object of the invention to provide improved methods and apparatus for balancing rotors.
It is a further object of the invention to provide methods and apparatus for producing and attaching precision balancing masses to compensate for unbalances in the rotor.